Image contrast analysis of STM images of self-assembled dioctadecyl chalcogenides on graphite at the liquid-solid interface.

The structures of self-assembled monolayers of dioctadecyl selenide (CH3(CH2)17)2Se and dioctadecyl telluride (CH3(CH2)17)2Te, as well as dioctadecyl ether (CH3(CH2)17)2O and dioctadecyl sulfide (CH3(CH2)17)2S, on graphite at the liquid-solid interface were systematically investigated by scanning tunneling microscopy (STM). Both dioctadecyl selenide and telluride formed monolayer structures in which the tilt angle between the molecular axis of the alkyl chain and the lamellae axis was 90 degrees , while dioctadecyl ether assembled with a tilt angle of 60 degrees . Dioctadecyl sulfide was found to make two different self-assembled structures having tilt angles of 60 and 90 degrees .